Conventionally, there is known a pretensioner for restricting an unpreferable forward movement of a seat occupant by rearwardly moving a vehicle seat when a large external force acts on a vehicle body by vehicle collision and the like.
When a collision detector detects vehicle collision, the conventional mechanism moves a vehicle seat in its entirety, that is, a seat bottom and a seatback rearward.    Patent Document 1: JP 2001-130354 A1